"Park Geun-Hye let loose a whole string of provocative remarks seriously hurting the dignity and social system in the DPRK (North Korea) while visiting China," the Committee for the Peaceful Reunification of Korea said in a statement through state media.
It was North Korea's first official reaction to a high-profile summit between its closest ally and South Korea during Park's four-day trip to China last week.
In China, Park called for the North's denuclearisation and described Pyongyang's policy of pushing forward economic construction together with its nuclear build-up as an unattainable goal.
"We have agreed that under any circumstances, North Korea's nuclear (weapons) are unacceptable," Park said after talks with Chinese President Xi Jinping.
The North's committee accused Park of making "so desperate efforts to garner support for South Korea that her shamelessness and disgusting nature reached the height".
"What merits a more serious attention is that Park ... dared take issue again with the DPRK's new strategic line during her trip," it said.
The committee denounced Park's remarks as "a blatant challenge to the dignity, social system and political line of the DPRK and an unpardonable grave provocation against it".
"Explicitly speaking once again, Park should clearly know that the DPRK's nukes, shield for justice and peace and treasure for the nation, can never be a bargaining chip in any case and they cannot be subject at a negotiating table no matter how vociferously the puppet group, war servants of the US, may talk about them," it said.
South Korea voiced regret over the North's statement and urged Pyongyang to exercise restraint.
"It's very regrettable," Unification Ministry spokesman Kim Hyung-Suk told reporters.
He said that for the sake of better relations, the North needs to modify what it says against the head of a country.
North Korea has shunned six-nation talks on its nuclear arsenal since late 2008. After testing an A-bomb again in February, it had severed ties with South Korea and issued apocalyptic threats as Seoul and Washington conducted joint war games.
In recent months, the North appeared to have moderated its stance.
After a proposed bridge-building meeting with Seoul failed to happen last month, Pyongyang proposed direct, high-level denuclearisation talks with Washington.
The North's offer was seen by many analysts as a bid to drive a wedge between the United States and its South Korean ally.
Washington responded by insisting that Pyongyang first demonstrate its willingness to abandon its nuclear weapons programme.